I have a 2001 accord ex 3.0L can I swap the ecu (same part #) without the ignition switch? Or do I need to get both?

 

PCM is paired with the key.
If it is from a junkyard see if they have the paired key to go with it. For a dirty fix you can keep your old key for the tumbler and just have your 'new' ecu key on your ring and it will work.
If you have a new/rebuilt PCM you will need to have the system programmed for your key.